1. Field of the Invention
Various embodiments relate generally to power distribution system and more specifically to a reliable low-cost hybrid switch module for providing a low cost and highly reliable smart switched power distribution system and method to use the same.
2. Description of the Related Art
It may be appreciated that power distribution system have been in use for years. Typically, switched power distribution systems sometime referred to as switched PDUs (power distribution unit) use either expensive solid state relays (SSRs) or cheaper electro-mechanical relays (EMRs) to switch power On/Off of individual outlets which distributes AC (alternating current) power to devices such as servers and switches found in typical datacenter racks. While these devices may be suitable for the particular purpose to which they address, they are not as suitable for providing highly reliable smart switched power distribution system and method to use the same for datacenter applications such as individual outlet level power distribution control, power monitoring, and management at affordable price.
The main problem with conventional EMR based power distribution system is its poor reliability due to contact bounce, especially with high current loads. The mechanical contact could produce arc when the electromagnetic relay controls a high voltage and large current flows that could lead to reduced contact lifetime—even contacts gel welded sometime. Usually the electrical lifetime may be about fifty to one hundred thousand times, but the mechanical lifetime may be over one million limes. Mechanical relays also produce electro-magnetic interferences and high power dissipation when switching large AC currents.
On the other hand, one of the main problem with SSR based PDUs is the cost. Another issue with SSR is that it waste power in the form of heat due to nominal voltage drop across semiconductor switching path. For example, SSR may consume more than 30 watts of power for a 20 A load per PDU. Typical midsize datacenter may have few hundreds of these PDUs so the thermal management not only bumps up the cost of PDU in terms of installing heat sinks but also increases the total cost of ownership for the end user in terms of power (HVAC or Heating, Ventilation, and Air Condition) wasted in cooling the heat produced by these PDUs. But to have a reliable PDU, so called hybrid relays may be used for each of the outlets but the cost of having such relays in a PDU doesn't justify the advantage of using them. It will become more expensive because a PDU may have multiple outlets ranging from four to 32 outlets sometimes even 64, as each outlet would require separate hybrid relay. The hybrid relays combine the benefits of an electro mechanical relay (EMR) and a solid-state relay (SSR) while reducing or eliminating the disadvantages of each. The cost of hybrid relay is high mainly because of the expensive SSR used in the package. An SSR is approximately 10 times more expensive than an EMR. A hybrid relay is two times more expensive than a SSR. That could be one of the reasons that the prior art of switched PDUs use either solid stale relays (SSR) or electro mechanical relays (EMR) to switch power On/Off for individual outlets of the PDU. The hybrid relay itself is not a new concept, the prior art hybrid relay has one EMR, a SSR and a controller integrated in one package.
These types of stand-alone hybrid relays prevent arcing of electro mechanical relays inside them and improves its lifetime. But these cannot scale for multiple outlets of a switched PDU without increasing the cost of switched PDU multiple limes.
Another problem with conventional power distribution system which provides power or current monitoring are that they use individual sensor and corresponding interface circuits for each outlet to do individual outlet power or current monitoring. This would bump up the cost of PDU because as discussed above there could be outlets up to 64 outlets per PDU which means 64 sensors and corresponding analog frontends.
Another problem with conventional power distribution system are that there is no individual outlet level overload protection with fast automatic recovery. There are only circuit breakers for overload protection at circuit level only which would require manual recovery.
In these respects, the reliable low-cost smart switched power distribution system using the hybrid switch module according to the various embodiments described herein substantially departs from the conventional concepts and designs of the prior art, by using only one SSR that is shared with all EMRs to provide switching reliability as good as a hybrid relay and cost as low as conventional PDUs, and in so doing provides an apparatus primarily developed for the purpose of providing a low cost and highly reliable smart switched power distribution system and method to use the same.